CDMA2000 promises to bring the first phase
of 3G services to market ahead of the mass UMTS camp, and
to do so with less disruption. But even a smoothly evolving
standard requires some changes and additions to the networks
employing it.By Leon Perlman

As the first major change to the cdmaOne technology that
has been implemented widely in the U.S. and Asia, it is important
that CDMA2000 works. If it does, it could persuade TDMA and
even some GSM operators in North America, China and Latin
America to provide a CDMA2000 overlay onto their existing
networks.

This first phase of the CDMA2000 upgrade, variously called
1XRTT, IMT MC1X, 3G1X, or just plain 1X, is designed to double
current voice capacity and support always-on data transmission
speeds ten times faster than those typically available today-some
153.6 kbit/s on both the forward and reverse links. Handset
standby times should also increase by up to 50 percent. Users,
meanwhile, will be able to benefit from enterprise and consumer
applications that would normally require more bandwidth, including
personal information management, telemetry, corporate intranet
access, videoconferencing, gaming and music on demand.

Voice and data capacity
The increase in voice and data capacity stems inter alia from
advances in modulation algorithms, new IP backbones, and new
chipsets that support up to 32 simultaneous users on a single
chip, a four-fold increase over the previous generation.

While the CDMA2000 specification allows for an evolutionary
migration to later advances in CDMA2000 that use core IP networks
and voice-over-IP, the current 1X migration requires relatively
modest hardware and software upgrades to existing cdmaOne
infrastructure. Even then, operators can upgrade to 1X without
having to implement it throughout their entire cdmaOne network,
which means they can upgrade certain hotspots that require
voice capacity enhancements or higher data speeds.

This strategy aims to reduce technological risks by phased
enhancements of networks with medium rate data services, and
then later evolve to higher rate data services so as to avoid
the uncertainties of return on investment that currently cloud
the UMTS 3G vision. UMTS operators have in many cases over-extended
themselves by paying billions of dollars for 3G spectrum to
provide high-speed data services which the CDMA2000 world
believes it can achieve without the same concomitant costs.

Of course, billions of dollars may well be spent by cdmaOne
operators to introduce CDMA2000 and its later iterations to
their customers. But that money won't (for the most part)
be spent on buying spectrum, since CDMA2000 follows an in-band
evolution strategy toward 3G based on existing worldwide cdmaOne
band classes and infrastructure. It can thus be deployed in
existing spectrum, overlaying its new feature sets and increased
capacity on existing cdmaOne networks, and using an existing
(and paid for) standard 1.25MHz frequency channel.

Efficiency
CDMA2000 maximizes the efficiency of the existing spectrum
and also recognizes the investments already made, all of which
results in significant benefits to operators. These benefits
include enhanced service provision, greater economies of scale,
reduced complexity, reduced time to deployment, and simplified
roaming, while delivering state-of-the art services to consumers.

Handsets using CDMA2000 technology will also be backward
compatible to existing cdmaOne networks, so current handsets
and features will operate over next generation networks providing
continued access both at home and while roaming. Operators
which deploy 3G with 1X will still have roaming with worldwide
CDMA operators on their cdmaOne networks. Dual mode handsets
that allow TDMA/CDMA2000 interoperability may also augment
the business case for a move by TDMA operators to CDMA2000.

The flexible migration from cdmaOne provides for a series
of upgrades leading to CDMA2000's increased voice capacity
and megabit data rates, allowing each operator to upgrade
when its individual market requirements dictate, without having
to significantly upgrade infrastructure or purchase new spectrum.
The evolution of the air interface, capability of the core
network (ANSI-41), and spectrum flexibility ensure this.

The business case that dictates the extent of its overlay
of their cdmaOne network will, of course, differ for each
carrier. This will depend on its capex spend and its capabilities,
as well as varying degrees of subscriber differentiation.
For some operators, the migration path may never need to reach
the megabit level, while others, especially those in Asia,
have a more immediate need to go as far down the 3G path as
possible.

From the operator perspective, there is relatively little
effort involved in upgrading a cdmaOne network to 1X. A 1X
upgrade does not require any hardware 'forklifting', just
some tweaking. They will be able to use most of their existing
infrastructure to allow backward compatibility to IS-95 users.

To permit the advanced multimedia services that a 1X implementation
promises, cdmaOne operators will have to do some retrofitting
of base station channel cards with 1X cards, implement software
upgrades in specific areas of their existing networks, and
add some new IP-centric boxes to allow them to implement the
data/voice 1X specification in part or in full. The approach
to this will differ in form depending on what vendor equipment
has been chosen, although most vendor approaches include ensuring
backward compatibility with existing base stations with flexible
future-proofing hooks for new technologies like intelligent
antennas to boost capacity.

What stays relatively intact in a 1X overlay of a cdmaOne
network is the MSC (mobile switching center), antenna systems,
amplifiers, filters, and the existing data core of IS-95 networks
called the IWF (inter working function). The IWF interfaces
to the MSC via a Lambda switch and allows cdmaOne terminals
access to a relatively limited packet data offering of around
9.6kbit/s. It is retained in a cdmaOne upgrade to 1X to provide
this backward data compatibility. The MSC, though, requires
a software upgrade.

At the base station level, new channel cards are required
to support the increased capacity and enhancement in IP provisioning.
New radio control software will also be required in the BS
to enable the new channels, and where appropriate, software
upgrades will also be necessary for base station controllers.
Some operators may, however, want to implement separate boxes
in the BSs in parallel with existing cdmaOne cards, primarily
for cdmaOne backwards compatibility, and 1X testing imperatives.

Support
The new software in the BSs and BSCs embody coherent reverse
link, additional Walsh code structures for more channels and
capacity and a new power control scheme, as well as a new
paging and synchronization channel messaging to allow users
to speed up access to new data facilities. 1X upgrades will
also support supplemental channel structures if voice and
data are used simultaneously and there is a need to increase
capacity of either at a given time and circumstance.

To complete the 1X data/voice picture, operators will have
to add additional hardware to define a new, comprehensive
always-on high-speed IP-centric environment lacking in cdmaOne
networks. Most of the new IP hardware in 1X systems is, unlike
the GPRS world, off-the-shelf and does not need to be specifically
designed or modified to exist in the wireless universe; this
ensures investment protection.

These new components-which will exist in parallel with the
IWF-include the PCF (packet control function) to act as an
interface to the MSC and to the PDSN (packet data service
node), another new 1X addition. The PDSN is a wireless-savvy
router that acts as an interface to the internet and intranets.

Another new addition is the AAA (accounting, authentication
and authorization) node which hangs off the PDSN to provide
service profiles of end-user-specific data for packet data
operations. The PCF was designed to allow the AAA and PDSN
to be as off-the-shelf as possible as to ensure interoperability,
and to allow a smooth transition to 3G services.

Soft switches
In later iterations of CDMA2000 1X, so-called 'soft switches'
will allow cdmaOne networks with 1X overlays to carry their
voice calls over IP in the backhaul, rather than the current
methodology that uses circuit switching.

TDMA networks wanting to overlay 1X will require, among other
things, new hybrid TDMA/CDMA2000 base stations, new BSC software,
new dual mode TDMA/CDMA2000 terminals for users, a new PDSN,
and new MSC software along with all the other components that
make up a 1X network. Although the 1X upgrade and later 1X-EV-DO/DV
iterations do not specifically require any increase in base
station numbers, because of the increased fidelity required
to maintain promised QoS speeds on the downlink and uplink,
and the need to ensure low latency for multimedia applications,
more BS and BSCs may in fact be necessary at the edge of the
networks where signal to noise (S/N) ratios impact on data
rates.

The necessity for improved amplifier and antenna systems
to produce the required fidelity might also arise in some
circumstances, although 1X promises up to 35 percent improvement
in coverage using existing base stations, filters, amplifiers,
and topography. It is anticipated that operators in densely
populated areas will want to get the full benefit of 1X by
upgrading to 1XEV where data demand is high.

Operators will also have to address voice capacity issues
with other technologies like smart antennas and dynamic power
control. The increase in RF capacity with 1X enables more
simultaneous users, which means increase in revenue per cell
site and higher return on investment, but also means that
operators will need to mediate between simultaneous higher
demand for voice and data.

The overlay design of 1X and its spectral efficiency protects
valuable voice revenue, as the provision of medium and high
rate IP-based services will not necessarily impact on voice
capacity. Operators will have the flexibility to support this
growing demand for voice and data without allocating bandwidth
specifically for data before customer demand requires it.

Some vendors allow operators to protect their voice revenues
by dedicating capacity to voice, which is usually given the
highest priority in the network. This could also encompass
throttling data rates up and down for users according to demand
and specific business models.

Peak, symmetrical data rates of 153.6kbit/s in ideal conditions
are possible, but field trails suggest that, as this is a
shared resource, 130kbit/s average aggregate throughput is
more likely. This will be shared by many users, which could
decrease available bandwidth to individual users, much like
heavy usage on an office LAN chocks individual demand. However,
since usage scenarios suggest the likelihood of more bursty-type
'surfing' where all of the available bandwidth is not swallowed
up in one gulp by a few users, fairly high throughputs nearing
130kbit/s are possible for individual users.

Billing information
The new AAA nodes will also be busy collecting varied types
of billing information, as operators devise new methods of
billing for the many new services anticipated to come on stream
as a result of the always-on, high-speed 1X capabilities.

The paradigm will thus change for pure time-based billing
to a combination of time and data usage. The billing scenarios
may include flat-rate models that bundle talk-and-surf, or
billing incorporating tiered levels of service with premium
billing for QoS assurances for data and voice quality.

These include QoS support via low delay tolerance, data rate
guarantee, and priority service access for multimedia applications.
Operators could offer premium voice quality to certain users
at a premium price using V2 voice mode (V1 is standard voice
quality). They may also be able to bill for 'hot spot' coverage
in convention centers, stadiums, malls and campuses, and for
dedicated data rates and coverage to groups of users.

It is also very likely that they will emulate the Japanese
i-mode success by taking a slice of profits for all micro-transactions
successfully completed over their networks and portals. This
in some cases will necessitate getting a banking partner or
even a banking license to allow users to create and maintain
mobile wallets for m-commerce payments on operator infrastructure.
Location-based services are also likely to enhance operator
revenues.

Later iterations of 1X will provide enhancements, such as
increased data rates, radio enhancements of transmit diversity,
smart antennas, direct spread, and multi-carrier, and inter-operation
of network protocols. These include 1X EV-DO, or 1X-EV Phase
One, which is a data-only enhancement to networks. Built primarily
upon Qualcomm's High Data Rate (HDR) technology, it places
voice and data on separate channels to provide up to 2.4Mbit/s
access speeds. Operators have to install an incremental carrier
in cell sites to provide these services. There's also the
controversial EV-DV, or 1X-EV Phase Two, which promises stratospheric
data speeds as high as three to 5Mbps. It requires a software
and digital card upgrade on the existing 1X network.

1X upgrades will also include implementation of industry
standard IOS V4 (version 4) interface to connect to the PDSN,
giving wireless operators the flexibility of selecting the
radio frequency (RF) mobile sub-system independently from
the MSC.

The building blocks to 3G have been assembled. CDMA2000 is
ready to go. Now it's time to put the new networks through
their paces.

This article first appeared in CDMA World Focus June 2001
published by Informa Telecoms. For more information
see www.telecoms.com